Of all the portable device displays on the market today, Apple has one of the most impressive with the Retina Display on the iPhone 4. It offers such a high resolution you can’t see the individual pixels while at the same time allowing multiple people to view content with wide viewing angles.

That’s all well and good when you want to share what’s on the screen with others, but what about those times when you are reading a private document, placing an order you don’t want your girlfriend to see, or just want to stop people looking over your shoulder at your beautiful screen?

At the moment, it’s a case of turning the display on your iPhone/iPod touch/iPad, and making sure no one is in viewing distance. In the future, Apple may provide you with an option to turn on a Privacy Mode, meaning no one but you can see what is on the screen of your device.

That Privacy Mode would require a new type of screen design, and that’s exactly what a new patent from the company covers in great detail.

Apple’s idea is to allow just about any LCD, LED, or OLED display to have this Privacy Mode applied. The method is complex, but relies on being able to control the direction of the light emanating from the display to the extent that it would only be viewable from a very small angle range. In other words, the person with the screen directly in front of them would be the only one seeing the content. This wouldn’t just be a setting, though, it seems Apple would allow the user to change that angle by some degrees.

The patent and technology behind this isn’t just limited to a physical screen. There’s also mention of projection being limited, too. So, for example, a future iPhone could have a pico projector embedded, but the angle of the light used in the projection limited so those around you can’t see it.

Whether we ever see it used in a device depends on just how easy it is to implement in existing screen tech, and whether it can be implemented reliably and without making a device thicker. From a user’s point of view, I’m sure we’d all appreciate the ability to make our displays more private at the touch of a button or tap of a screen.